Magnetic Field Sensor and Electronic Circuit That Pass Amplifier Current Through a Magnetoresistance Element

ABSTRACT

Electronic circuits used in magnetic field sensors use transistors for passing a current through the transistors and also through a magnetoresistance element.

CROSS REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to magnetic field sensors and, moreparticularly, to a magnetic field sensor, or an electronic circuit usedtherein, that pass an amplifier supply current through a magnetic fieldsensing element.

BACKGROUND

Magnetoresistance elements are known. A magnetoresistance elementchanges resistance in response to a magnetic field. Magnetic fieldsensors having electronic circuits coupled to the magnetoresistanceelement can inject a current into the magnetoresistance element and usea voltage resulting across the magnetoresistance element as beingrepresentative of a sensed magnetic field.

Conventionally, the current used to drive the magnetoresistance elementuses power.

It would be desirable to provide a magnetic field sensor and associatedelectronic circuit for which a magnetoresistance element requires noextra power beyond that which is otherwise used by the magnetic fieldsensor.

SUMMARY

The present invention provides a magnetic field sensor and associatedelectronic circuit for which a magnetoresistance element requires noextra power beyond that which is otherwise used by the magnetic fieldsensor.

In accordance with an example useful for understanding an aspect of thepresent invention, an electronic circuit includes a firstmagnetoresistance element having first and second terminals. Theelectronic circuit also includes a first transistor having a controlnode, a first current passing node, and a second current passing node.The electronic circuit also includes a first voltage source having firstand second nodes between which a first voltage is generated. The firstterminal of the first magnetoresistance element is coupled to the firstcurrent passing node of the first transistor. The first node of thefirst voltage source is coupled to the control node of the firsttransistor and the second node of the first voltage source is coupled tothe second terminal of the first magnetoresistance element. Theelectronic circuit is operable to generate a first current signal at thesecond current passing node of the first transistor related to aresistance value of the first magnetoresistance element.

In accordance with another example useful for understanding an aspect ofthe present invention, a magnetic field sensor includes a substrate andan electronic circuit disposed upon the substrate. The electroniccircuit includes a first magnetoresistance element having first andsecond terminals. The electronic circuit further includes a firsttransistor having a control node, a first current passing node, and asecond current passing node. The electronic circuit further includes afirst voltage source having first and second nodes between which a firstvoltage is generated, wherein the first terminal of the firstmagnetoresistance element is coupled to the first current passing nodeof the first transistor, and wherein the first node of the first voltagesource is coupled to the control node of the first transistor and thesecond node of the first voltage source is coupled to the secondterminal of the first magnetoresistance element. The electronic circuitis operable to generate a first current signal at the second currentpassing node of the first transistor related to a resistance value ofthe first magnetoresistance element. The electronic circuit furtherincludes a second magnetoresistance element having first and secondterminals and a second transistor having a control node, a first currentpassing node, and a second current passing node. The electronic circuitfurther includes a second voltage source having first and second nodesbetween which a second voltage is generated. The electronic circuitfurther includes a load coupled to the second current passing node ofthe first transistor, wherein the second current passing node of thefirst transistor is coupled to the second current passing node of thesecond transistor. The first terminal of the second magnetoresistanceelement is coupled to the first current passing node of the secondtransistor. The first node of the second voltage source is coupled tothe control node of the second transistor and the second node of thesecond voltage source is coupled to the second terminal of the secondmagnetoresistance element. The electronic circuit is operable togenerate a second current signal at the second current passing node ofthe second transistor related to a resistance value of the secondmagnetoresistance element, wherein a current passing through the load isequal to a difference between the first current signal and the secondcurrent signal.

In accordance with another example useful for understanding an aspect ofthe present invention, a magnetic field sensor includes a substrate andan electronic circuit disposed upon the substrate. The electroniccircuit includes a first magnetoresistance element having first andsecond terminals and a first transistor having a control node, and firstcurrent passing node, and a second current passing node. The electroniccircuit further includes a first voltage source having first and secondnodes between which a first voltage is generated. The first terminal ofthe first magnetoresistance element is coupled to the first currentpassing node of the first transistor. The first node of the firstvoltage source is coupled to the control node of the first transistorand the second node of the first voltage source is coupled to the secondterminal of the first magnetoresistance element. The electronic circuitis operable to generate a first current signal at the second currentpassing node of the first transistor related to a resistance value ofthe first magnetoresistance element. The electronic circuit furtherincludes a second magnetoresistance element having first and secondterminals and a second transistor having a control node, a first currentpassing node, and a second current passing node. The electronic circuitfurther includes a second voltage source having first and second nodesbetween which a second voltage is generated. The electronic circuitfurther includes a load coupled to the second current passing node ofthe first transistor. The second current passing node of the firsttransistor is coupled to the second current passing node of the secondtransistor. The first terminal of the second magnetoresistance elementis coupled to the first current passing node of the second transistor.The first node of the second voltage source is coupled to the controlnode of the second transistor and the second node of the second voltagesource is coupled to the second terminal of the second magnetoresistanceelement. The electronic circuit is operable to generate a second currentsignal at the second current passing node of the second transistorrelated to a resistance value of the second magnetoresistance element. Acurrent passing through the load is equal to a difference between thefirst current signal and the second current signal. The electroniccircuit further includes a third magnetoresistance element having firstand second terminals and a third transistor having a control node, andfirst current passing node, and a second current passing node. Theelectronic circuit further includes a third voltage source having firstand second nodes between which a third voltage is generated. The firstterminal of the third magnetoresistance element is coupled to the firstcurrent passing node of the third transistor. The first node of thethird voltage source is coupled to the control node of the thirdtransistor and the second node of the third voltage source is coupled tothe second terminal of the third magnetoresistance element. Theelectronic circuit is operable to generate a third current signal at thesecond current passing node of the third transistor related to aresistance value of the third magnetoresistance element. The electroniccircuit further includes a fourth magnetoresistance element having firstand second terminals and a fourth transistor having a control node, afirst current passing node, and a second current passing node. Theelectronic circuit further includes a fourth voltage source having firstand second nodes between which a fourth voltage is generated. Theelectronic circuit further includes a second load coupled to the secondcurrent passing node of the third transistor. The second current passingnode of the third transistor is coupled to the second current passingnode of the fourth transistor. The first terminal of the fourthmagnetoresistance element is coupled to the first current passing nodeof the fourth transistor. The first node of the fourth voltage source iscoupled to the control node of the fourth transistor and the second nodeof the fourth voltage source is coupled to the second terminal of thefourth magnetoresistance element. The electronic circuit is operable togenerate a fourth current signal at the second current passing node ofthe fourth transistor related to a resistance value of the fourthmagnetoresistance element, wherein a current passing through the secondload is equal to a difference between the third current signal and thefourth current signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is a schematic diagram of an example of an electronic circuit asmay be used in a magnetic field sensor, and which has or is otherwisecoupled to one magnetoresistance element;

FIG. 2 is a schematic diagram of another example of an electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to one magnetoresistance element;

FIG. 3 is a schematic diagram of another example of an electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to one magnetoresistance element;

FIG. 4 is a schematic diagram of another example of an electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to one magnetoresistance element;

FIG. 5 is a schematic diagram of another example of an electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to one magnetoresistance element;

FIG. 6 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to one magnetoresistance element;

FIG. 7 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to two magnetoresistance elements;

FIG. 8 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to two magnetoresistance elements;

FIG. 9 is a block diagram of a magnetic field sensor having a substratewith two magnetoresistance elements disposed thereon, the substratedisposed proximate to a ferromagnetic target object having ferromagnetictarget object features;

FIG. 10 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to four magnetoresistance elements;

FIG. 11 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to four magnetoresistance elements;

FIG. 12 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to four magnetoresistance elements;

FIG. 13 is a block diagram of a magnetic field sensor having a substratewith four magnetoresistance elements disposed thereon, the substratedisposed proximate to a ferromagnetic target object having ferromagnetictarget object features;

FIG. 14 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to eight magnetoresistance elements;

FIG. 15 is a block diagram of a magnetic field sensor having a substratewith eight magnetoresistance elements disposed thereon, the substratedisposed proximate to a ferromagnetic target object having ferromagnetictarget object features;

FIG. 16 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to four magnetoresistance elements; and

FIG. 17 is a schematic diagram of an example of another electroniccircuit as may be used in another magnetic field sensor, and which hasor is otherwise coupled to four magnetoresistance elements.

DETAILED DESCRIPTION

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, for example, a spinvalve, an anisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).The magnetic field sensing element may be a single element or,alternatively, may include two or more magnetic field sensing elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. Depending on the device type and other applicationrequirements, the magnetic field sensing element may be a device made ofa type IV semiconductor material such as Silicon (Si) or Germanium (Ge),or a type III-V semiconductor material like Gallium-Arsenide (GaAs) oran Indium compound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elementstend to have an axis of maximum sensitivity parallel to a substrate thatsupports the magnetic field sensing element, and others of theabove-described magnetic field sensing elements tend to have an axis ofmaximum sensitivity perpendicular to a substrate that supports themagnetic field sensing element. In particular, planar Hall elements tendto have axes of sensitivity perpendicular to a substrate, while metalbased or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) andvertical Hall elements tend to have axes of sensitivity parallel to asubstrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-biased or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

As used herein, the term “processor” is used to describe an electroniccircuit that performs a function, an operation, or a sequence ofoperations. The function, operation, or sequence of operations can behard coded into the electronic circuit or soft coded by way ofinstructions held in a memory device. A “processor” can perform thefunction, operation, or sequence of operations using digital values orusing analog signals.

In some embodiments, the “processor” can be embodied in an applicationspecific integrated circuit (ASIC), which can be an analog ASIC or adigital ASIC. In some embodiments, the “processor” can be embodied in amicroprocessor with associated program memory. In some embodiments, the“processor” can be embodied in a discrete electronic circuit, which canbe an analog or digital.

As used herein, the term “module” is used to describe a “processor.”

A processor can contain internal processors or internal modules thatperform portions of the function, operation, or sequence of operationsof the processor. Similarly, a module can contain internal processors orinternal modules that perform portions of the function, operation, orsequence of operations of the module.

As used herein, the term “predetermined,” when referring to a value orsignal, is used to refer to a value or signal that is set, or fixed, inthe factory at the time of manufacture, or by external means, e.g.,programming, thereafter. As used herein, the term “determined,” whenreferring to a value or signal, is used to refer to a value or signalthat is identified by a circuit during operation, after manufacture.

As used herein, the term “active electronic component” is used todescribe and electronic component that has at least one p-n junction. Atransistor, a diode, and a logic gate are examples of active electroniccomponents. In contrast, as used herein, the term “passive electroniccomponent” as used to describe an electronic component that does nothave at least one p-n junction. A capacitor and a resistor are examplesof passive electronic components.

While electronic circuit shown in figures herein may be shown in theform of analog blocks or digital blocks, it will be understood that theanalog blocks can be replaced by digital blocks that perform the same orsimilar functions and the digital blocks can be replaced by analogblocks that perform the same or similar functions.

Both bipolar junction transistors (BJTs) (or more simply, bipolartransistors) and field effect transistors (FETs) are used in examplesherein. It should be understood that, for a bipolar transistor, most ofthe current flowing through the bipolar transistor flows between acollector terminal and an emitter terminal. Similarly, it should beunderstood that, for a field effect transistor, most of the currentflowing through the field effect transistor flows between a drainterminal and a source terminal. Therefore, for bipolar transistors, thecollector terminal and the emitter terminal are both sometimes referredto herein as “current passing terminals.” Similarly, for field effecttransistors, the drain terminal and the source terminal are also bothsometimes referred to herein as “current passing terminals.”

It should be also understood that the current flowing through a bipolartransistor is controlled by a current at a base terminal. Similarly, itshould be understood that the current flowing through a field effecttransistor is controlled by a voltage at a gate terminal. Thus, forbipolar transistors, the base terminal is sometimes referred to hereinas a “control terminal.” Similarly, for field effect transistors, thegate terminal is sometimes also referred to herein as a “controlterminal.”

Both current sources and current sinks are described herein. As usedherein, the term “current generator” is used to describe either acurrent source or a current sink.

Referring to FIG. 1, an example of an electronic circuit 100 can be usedin a magnetic field sensor. The electronic circuit 100 can include afixed resistor 106 having first and second terminals, wherein the firstterminal of the resistor 106 is coupled to receive a voltage 102 and thesecond terminal of the resistor 106 is coupled to an emitter of a PNPbipolar transistor 108.

The electronic circuit 100 can include a voltage source 104 having firstand second terminals, wherein the first terminal of the voltage source104 is coupled to receive the voltage 102 and the second terminal of thevoltage source 104 is coupled to a base of the PNP bipolar transistor108.

The electronic circuit 100 can also include a magnetoresistance element110 having first and second terminals, wherein the first terminal of themagnetoresistance element 110 is coupled to a collector of the PNPbipolar transistor 108 and the second terminal of the magnetoresistanceelement 110 is coupled to a voltage reference, for example, a groundvoltage.

An output voltage 112 can be generated at the collector of the PNPbipolar transistor 108.

In some embodiments, the electronic circuit 100 can include a comparator114 having first and second input terminals, wherein a first inputterminal of the comparator 114 is coupled to the collector of the PNPbipolar transistor 108 and the second input terminal of the comparator114 is coupled to receive a threshold voltage 116. The comparator 114can be configured to generate a comparison signal 118. The comparisonsignal 118 can have two states.

It will be understood that, for embodiments here and below that use acomparator, the associated electronic circuits form an electronicswitch, wherein a state of the comparison signal 118 is determined by astrength of a magnetic field experienced by the magnetoresistanceelement 110. It should also be understood that embodiments shown belowthat are not shown to include a comparator can be adapted to use acomparator to provide an electronic switch.

It should be appreciated that the voltage source 104, the resistor 106,and the PNP bipolar transistor 108 form a current source operable toprovide a fixed current, I, to the magnetoresistance element 110. Thus,the output voltage 112 is generated according to the followingrelationships. In this and in all equations that follow in conjunctionwith other figures below, a base current of bipolar transistors isrelatively small and is disregarded.

$\begin{matrix}\begin{matrix}{{Vout} = {I \times A}} \\{= {{\left( {V - {Vbe}} \right)/R} \times A}}\end{matrix} & (1)\end{matrix}$

where:

V=voltage of voltage source 204

R=resistance of resistor 106

A=resistance of the magnetoresistance element 110

Vbe=base emitter voltage of PNP bipolar transistor 108=approx. 0.7 volts

In the electronic circuit 100, it should be appreciated that the samecurrent, I. flows through the PNP bipolar transistor 108 and through themagnetoresistance element 110.

Referring now to FIG. 2, another example of an electronic circuit 200can be used in another magnetic field sensor. The electronic circuit 200can include a magnetoresistance element 206 having first and secondterminals, wherein the first terminal of the magnetoresistance element206 is coupled to receive a voltage 202 and the second terminal of themagnetoresistance element 206 is coupled to an emitter of a PNP bipolartransistor 208.

The electronic circuit 200 can include a voltage source 204 having firstand second terminals, wherein the first terminal of the voltage source204 is coupled to receive the voltage 202 and the second terminal of thevoltage source 104 is coupled to a base of the PNP bipolar transistor208.

The electronic circuit 200 can include a resistor 210 having first andsecond terminals, wherein the first terminal of the resistor 210 iscoupled to a collector of the PNP bipolar transistor 208 and the secondterminal of the resistor 210 is coupled to a voltage reference, forexample, a ground voltage.

An output voltage 212 can be generated at the collector of the PNPbipolar transistor 208.

In some embodiments, the electronic circuit 200 can include a comparator214 having first and second input terminals, wherein a first inputterminal of the comparator 214 is coupled to the collector of the PNPbipolar transistor 208 and the second input terminal of the comparator214 is coupled to receive a threshold voltage 216. The comparator 214can be configured to generate a comparison signal 218.

It should be appreciated that the voltage source 204, themagnetoresistance element 206, and the PNP bipolar transistor 208 form avariable current source operable to provide a variable current, I, tothe resistor 110. The variable current, I, varies in accordance with avariable resistance of the magnetoresistance element 206, which variesin accordance with a sensed magnetic field. Thus, the output voltage 112is generated according to the following:

$\begin{matrix}\begin{matrix}{{Vout} = {I \times R}} \\{= {{\left( {V - {Vbe}} \right)/A} \times R}}\end{matrix} & (2)\end{matrix}$

where:

V=voltage of voltage source 204

R=resistance of resistor 210

A=resistance of the magnetoresistance element 206

Vbe=base emitter voltage of PNP bipolar transistor 208=approx. 0.7 volts

In the electronic circuit 200, it should be appreciated that the samecurrent, I, flows through the PNP bipolar transistor 208 and through themagnetoresistance element 206.

Referring to FIG. 3, another example of an electronic circuit 300 can beused in another magnetic field sensor. The electronic circuit 300 caninclude a magnetoresistance element 304 having first and secondterminals, wherein the first terminal of the magnetoresistance element304 is coupled to receive a voltage 302 and the second terminal of themagnetoresistance element 304 is coupled to a collector of an NPNbipolar transistor 306.

The electronic circuit 300 can include a resistor 308 having first andsecond terminals, wherein the first terminal of the resistor 308 iscoupled to an emitter of the NPN bipolar transistor 306 and the secondterminal of the resistor 308 is coupled to a reference voltage, forexample, a ground reference voltage.

The electronic circuit 300 can include a voltage source 310 having firstand second terminals, wherein the first terminal of the voltage source310 is coupled to a base of the NPN bipolar transistor 306 and thesecond terminal of the voltage source 310 is coupled to the secondterminal of the resistor 308.

An output voltage 312 can be generated at the collector of the NPNbipolar transistor 306.

In some embodiments, the electronic circuit 300 can include a comparator314 having first and second input terminals, wherein a first inputterminal of the comparator 314 is coupled to the collector of the NPNbipolar transistor 306 and the second input terminal of the comparator314 is coupled to receive a threshold voltage 316. The comparator 314can be configured to generate a comparison signal 318.

It should be appreciated that the voltage source 310, the resistor 308,and the NPN bipolar transistor 306 form a current sink operable toprovide a fixed current, I, to the magnetoresistance element 304. Thus,the output voltage 312 is generated according to the following:

$\begin{matrix}\begin{matrix}{{Vout} = {I \times A}} \\{= {{\left( {V - {Vbe}} \right)/R} \times A}}\end{matrix} & (3)\end{matrix}$

where:

V=voltage of voltage source 310

R=resistance of resistor 308

A=resistance of the magnetoresistance element 304

Vbe=base emitter voltage of NPN bipolar transistor 306=approx. 0.7 volts

In the electronic circuit 300, it should be appreciated that the samecurrent, I. flows through the NPN bipolar transistor 306 and through themagnetoresistance element 304.

Referring now to FIG. 4, another example of an electronic circuit 400can be used in another magnetic field sensor. The electronic circuit 400can include a resistor 404 having first and second terminals, whereinthe first terminal of the resistor 404 is coupled to receive a voltage402 and the second terminal of the resistor 404 is coupled to acollector of an NPN bipolar transistor 406.

The electronic circuit 400 can include a magnetoresistance element 408having first and second terminals, wherein the first terminal of themagnetoresistance element 408 is coupled to an emitter of the NPNbipolar transistor 406 and the second terminal of the magnetoresistanceelement 408 is coupled to a reference voltage, for example, a groundreference voltage.

The electronic circuit 400 can include a voltage source 410 having firstand second terminals, wherein the first terminal of the voltage source410 is coupled to a base of the NPN bipolar transistor 408 and thesecond terminal of the voltage source 410 is coupled to the secondterminal of the magnetoresistance element 408

An output voltage 412 can be generated at the collector of the NPNbipolar transistor 406.

In some embodiments, the electronic circuit 400 can include a comparator414 having first and second input terminals, wherein a first inputterminal of the comparator 414 is coupled to the collector of the NPNbipolar transistor 406 and the second input terminal of the comparator414 is coupled to receive a threshold voltage 416. The comparator 414can be configured to generate a comparison signal 418.

It should be appreciated that the voltage source 410, themagnetoresistance element 408, and the NPN bipolar transistor 406 form avariable current sink operable to provide a variable current, I, to theresistor 404. The variable current, I, varies in accordance with avariable resistance of the magnetoresistance element 408, which variesin accordance with a sensed magnetic field. Thus, the output voltage 412is generated according to the following:

$\begin{matrix}\begin{matrix}{{Vout} = {I \times R}} \\{= {{\left( {V - {Vbe}} \right)/A} \times R}}\end{matrix} & (4)\end{matrix}$

where:

V=voltage of voltage source 410

R=resistance of resistor 404

A=resistance of the magnetoresistance element 408

Vbe=base emitter voltage of PNP bipolar transistor 406=approx. 0.7 volts

In the electronic circuit 400, it should be appreciated that the samecurrent, I. flows through the NPN bipolar transistor 406 and through themagnetoresistance element 408.

Referring now to FIG. 5, another example of an electronic circuit 500can be used in another magnetic field sensor. The electronic circuit 500can include a magnetoresistance element 506 having first and secondterminals, wherein the first terminal of the magnetoresistance element506 is coupled to receive a voltage 502 and the second terminal of themagnetoresistance element 506 is coupled to an emitter of a PNP bipolartransistor 508.

The electronic circuit 500 can include a voltage source 504 having firstand second terminals, wherein the first terminal of the voltage source504 is coupled to receive the voltage 502 and the second terminal of thevoltage source 504 is coupled to a base of the PNP bipolar transistor508.

The electronic circuit 500 can include a resistor 514 having first andsecond terminals, wherein the first terminal of the resistor 514 iscoupled to an emitter of an NPN bipolar transistor 510 and the secondterminal of the resistor 514 is coupled to a voltage reference, forexample, a ground voltage.

The electronic circuit 500 can include another voltage source 512 havingfirst and second terminals, wherein the first terminal of the voltagesource 512 is coupled a base of the NPN bipolar transistor 510 and thesecond terminal of the voltage source 512 is coupled to the secondterminal of the resistor 514.

A collector of the PNP bipolar transistor 508 can be coupled to acollector of the NPN bipolar transistor 510 at a junction node.

A load 518, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 518.

The load 518 is labeled Zload. The nomenclature, Zload, used here and infigures below is not intended to limit the load 518 or loads discussedbelow to one or more passive electronic components. Instead, the load518 and loads discussed below can be comprised of passive electroniccomponents, active electronic components, or both.

An output voltage 516 can be generated at the collector of the PNPbipolar transistor 508 (i.e., at the junction node).

In some embodiments, the electronic circuit 500 can include a comparatorcoupled to the junction node that is the same as or similar to thecomparators shown above in conjunction with FIGS. 1-4.

It should be appreciated that the voltage source 504, themagnetoresistance element 506, and the PNP bipolar transistor 508 form avariable current source operable to provide a variable current, I1. Thevariable current, I1, varies in accordance with a variable resistance ofthe magnetoresistance element 506, which varies in accordance with asensed magnetic field. It should be appreciated that the voltage source512, the resistor 514, and the NPN bipolar transistor 510 form a currentsink operable to provide a fixed current, I2. Thus, the output voltage516 is generated according to the following:

Vout=Vb+[(I1−I2)×Zload]

I1=(V1−Vbe)/A

I2=(V2−Vbe)/R

I1−I2=(V1−Vbe)/A−(V2−Vbe)/R

Vout=Vb+[[(V1−Vbe)/A−(V2−Vbe)/R]×Zload]  (5)

where:

-   -   V1=voltage of voltage source 504    -   V2=voltage of voltage source 512    -   R=resistance of resistor 514    -   A=resistance of the magnetoresistance element 506    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 508 and of        NPN bipolar transistor 510=approx. 0.7 volts

It should be understood that the load 518 can be made to have a highimpedance to achieve a gain not obtained with the electronic circuits ofFIGS. 1-4 described above.

In the electronic circuit 500, it should be appreciated that the samecurrent, I1, flows through the PNP bipolar transistor 508 and throughthe magnetoresistance element 506.

Referring now to FIG. 6, another example of an electronic circuit 600can be used in another magnetic field sensor. The electronic circuit 600can include a resistor 606 having first and second terminals, whereinthe first terminal of the resistor 606 is coupled to receive a voltage602 and the second terminal of the resistor 606 is coupled to an emitterof a PNP bipolar transistor 608.

The electronic circuit 600 can include a voltage source 604 having firstand second terminals, wherein the first terminal of the voltage source604 is coupled to receive the voltage 602 and the second terminal of thevoltage source 604 is coupled to a base of the PNP bipolar transistor608.

The electronic circuit 600 can include a magnetoresistance element 614having first and second terminals, wherein the first terminal of themagnetoresistance element 614 is coupled to an emitter of an NPN bipolartransistor 610 and the second terminal of the magnetoresistance element614 is coupled to a voltage reference, for example, a ground voltage.

The electronic circuit 600 can include another voltage source 612 havingfirst and second terminals, wherein the first terminal of the voltagesource 612 is coupled a base of the NPN bipolar transistor 610 and thesecond terminal of the voltage source 612 is coupled to the secondterminal of the magnetoresistance element 614.

A collector of the PNP bipolar transistor 608 can be coupled to acollector of the NPN bipolar transistor 610 at a junction node.

A load 618, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 618.

The load 618 is labeled Zload. The nomenclature, Zload, used here and infigures below is not intended to limit the load 618 or loads discussedbelow to one or more passive electronic components. Instead, the load618 and loads discussed below can be comprised of passive electroniccomponents, active electronic components, or both.

An output voltage 616 can be generated at the collector of the PNPbipolar transistor 608 (i.e., at the junction node).

In some embodiments, the electronic circuit 600 can include a comparatorcoupled to the junction node that is the same as or similar to thecomparators shown above in conjunction with FIGS. 1-4. Other electroniccircuits described below can also include a comparator, though notshown.

It should be appreciated that the voltage source 604, the resistor 606,and the PNP bipolar transistor 608 form a current source operable toprovide a fixed current, I1. It should be appreciated that the voltagesource 612, the magnetoresistance element 614, and the NPN bipolartransistor 610 form a variable current sink operable to provide avariable current, I2. The variable current, I2, varies in accordancewith a variable resistance of the magnetoresistance element 614, whichvaries in accordance with a sensed magnetic field.

Thus, the output voltage 616 is generated according to the following:

Vout=Vb+[(I1−I2)×Zload]

I1=(V1−Vbe)/R

I2=(V2−Vbe)/A

I1−I2=(V1−Vbe)/R−(V2−Vbe)/A

Vout=Vb+[[(V1−Vbe)/R−(V2−Vbe)/A]×Zload]  (6)

where:

-   -   V1=voltage of voltage source 604    -   V2=voltage of voltage source 612    -   R=resistance of resistor 606    -   A=resistance of the magnetoresistance element 614    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 608 and of        NPN bipolar transistor 610=approx. 0.7 volts

It should be understood that the load 618 can be made to have a highimpedance to achieve a gain not obtained with the electronic circuits ofFIGS. 1-4 described above.

In the electronic circuit 600, it should be appreciated that the samecurrent, I2, flows through the NPN bipolar transistor 610 and throughthe magnetoresistance element 614.

Referring now to FIG. 7, another example of an electronic circuit 700can be used in another magnetic field sensor. The electronic circuit 700can include a magnetoresistance element 706 having first and secondterminals, wherein the first terminal of the magnetoresistance element706 is coupled to receive a voltage 702 and the second terminal of themagnetoresistance element 706 is coupled to an emitter of a PNP bipolartransistor 708.

The electronic circuit 700 can include a voltage source 704 having firstand second terminals, wherein the first terminal of the voltage source704 is coupled to receive the voltage 702 and the second terminal of thevoltage source 704 is coupled to a base of the PNP bipolar transistor708.

The electronic circuit 700 can include another magnetoresistance element714 having first and second terminals, wherein the first terminal of themagnetoresistance element 714 is coupled to an emitter of an NPN bipolartransistor 710 and the second terminal of the magnetoresistance element714 is coupled to a voltage reference, for example, a ground voltage.

The electronic circuit 700 can include another voltage source 712 havingfirst and second terminals, wherein the first terminal of the voltagesource 712 is coupled a base of the NPN bipolar transistor 710 and thesecond terminal of the voltage source 712 is coupled to the secondterminal of the magnetoresistance element 714.

A collector of the PNP bipolar transistor 708 can be coupled to acollector of the NPN bipolar transistor 710 at a junction node.

A load 718, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 718.

The load 718 is labeled Zload. The nomenclature, Zload, used here and infigures below is not intended to limit the load 718 or loads discussedbelow to one or more passive electronic components. Instead, the load718 and loads discussed below can be comprised of passive electroniccomponents, active electronic components, or both.

An output voltage 716 can be generated at the collector of the PNPbipolar transistor 708 (i.e., at the junction node).

In some embodiments, the electronic circuit 700 can include a comparatorcoupled to the junction node that is the same as or similar to thecomparators shown above in conjunction with FIGS. 1-4. Other electroniccircuits described below can also include a comparator, though not shownor described below.

It should be appreciated that the voltage source 704, themagnetoresistance element 706, and the PNP bipolar transistor 708 form avariable current source operable to provide a variable current, I1. Thevariable current, I1, varies in accordance with a variable resistance ofthe magnetoresistance element 706, which varies in accordance with asensed magnetic field. It should be appreciated that the voltage source712, the magnetoresistance element 714, and the NPN bipolar transistor710 form a variable current sink operable to provide a variable current,I2. The variable current, I2, varies in accordance with a variableresistance of the magnetoresistance element 714, which varies inaccordance with a sensed magnetic field.

Thus, the output voltage 716 is generated according to the following:

Vout=Vb+[(I1−I2)×Zload]

I1=(V1−Vbe)/A

I2=(V2−Vbe)/B

I1−I2=(V1−Vbe)/R−(V2−Vbe)/A

Vout=Vb+[[(V1−Vbe)/A−(V2−Vbe)/B]×Zload]  (7)

where:

-   -   V1=voltage of voltage source 704    -   V2=voltage of voltage source 712    -   A=resistance of magnetoresistance element 706    -   B=resistance of the magnetoresistance element 714    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 706 and of        NPN bipolar transistor 710=approx. 0.7 volts

It should be understood that the load 718 can be made to have a highimpedance to achieve a gain not obtained with the electronic circuits ofFIGS. 1-4 described above.

In the electronic circuit 700, noises of the two magnetoresistanceelements 706, 714 add incoherently to result in the square root of twotimes the noise of one magnetoresistance element. However, signalsresulting from resistance changes of the two magnetoresistance elements706, 714 add coherently to result in an output signal 716 two times asignal that would result from one magnetoresistance element, forexample, as provided by the electronic circuits of FIGS. 1-6. Thus, asignal to noise ratio improvement is obtained. Similar improvements insignal to noise ratio can be obtained for similar reasons with circuitsdescribed below.

In the electronic circuit 700, it should be appreciated that the samecurrent, I1, flows through the PNP bipolar transistor 708 and throughthe magnetoresistance element 706. Also, the same current, I2, flowsthrough the NPN bipolar transistor 710 and through the magnetoresistanceelement 714.

Referring now to FIG. 8, another example of an electronic circuit 800can be used in another magnetic field sensor. The electronic circuit 800can include a magnetoresistance element 806 having first and secondterminals, wherein the first terminal of the magnetoresistance element806 is coupled to receive a voltage 802 and the second terminal of themagnetoresistance element 806 is coupled to an emitter of a PNP bipolartransistor 808.

The electronic circuit 800 can include a voltage source 804 having firstand second terminals, wherein the first terminal of the voltage source804 is coupled to receive the voltage 802 and the second terminal of thevoltage source 804 is coupled to a base of the PNP bipolar transistor808.

The electronic circuit 800 can include a resistor 814 having first andsecond terminals, wherein the first terminal of the resistor 814 iscoupled to an emitter of an NPN bipolar transistor 810 and the secondterminal of the resistor 814 is coupled to a voltage reference, forexample, a ground voltage.

The electronic circuit 800 can include another voltage source 812 havingfirst and second terminals, wherein the first terminal of the voltagesource 812 is coupled a base of the NPN bipolar transistor 810 and thesecond terminal of the voltage source 812 is coupled to the secondterminal of the resistor 814.

A collector of the PNP bipolar transistor 808 can be coupled to acollector of the NPN bipolar transistor 810 at a junction node.

A load 818, which can be a resistive or a complex load, can be coupledbetween the junction node and the second terminal of the resistor 814.

An output voltage 816 can be generated at the collector of the PNPbipolar transistor 808 (i.e., at the junction node).

It should be appreciated that the voltage source 804, themagnetoresistance element 806, and the PNP bipolar transistor 808 form avariable current source operable to provide a variable current, I1. Thevariable current, I1, varies in accordance with a variable resistance ofthe magnetoresistance element 806, which varies in accordance with asensed magnetic field. It should be appreciated that the voltage source812, the resistor 814, and the NPN bipolar transistor 810 form a currentsink operable to provide a fixed current, I2. Thus, the output voltage816 is generated according to the following:

Vout1=Vb+[(I1−I2)×Zload1]

I1=(V1−Vbe)/A

I2=(V2−Vbe)/R1

I1−I2=(V1−Vbe)/A−(V2−Vbe)/R1

Vout1=Vb+[[(V1−Vbe)/A−(V2−Vbe)/R1]×Zload1]  (8)

where:

-   -   Zload1=impedance of load 818    -   Vout1=voltage 816    -   V1=voltage of voltage source 804    -   V2=voltage of voltage source 812    -   R1=resistance of resistor 814    -   A=resistance of the magnetoresistance element 806    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 808 and of        NPN bipolar transistor 810=approx. 0.7 volts

In the electronic circuit 800, it should be appreciated that the samecurrent, I1 flows through the PNP bipolar transistor 808 and through themagnetoresistance element 806.

The electronic circuit 800 can also include a resistor 820 having firstand second terminals, wherein the first terminal of the resistor 820 iscoupled to receive the voltage 802 and the second terminal of theresistor 820 is coupled to an emitter of a PNP bipolar transistor 822.

The second terminal of the voltage source 804 can be coupled to a baseof the PNP bipolar transistor 822.

The electronic circuit 800 can include a magnetoresistance element 826having first and second terminals, wherein the first terminal of themagnetoresistance element 826 is coupled to an emitter of an NPN bipolartransistor 824 and the second terminal of the magnetoresistance element826 is coupled to a voltage reference, for example, a ground voltage.

The first terminal of the voltage source 812 is coupled a base of theNPN bipolar transistor 824.

A collector of the PNP bipolar transistor 822 can be coupled to acollector of the NPN bipolar transistor 824 at a junction node.

A load 830, which can be a resistive or a complex load, can be coupledbetween the junction node and the second terminal of themagnetoresistance element 826.

An output voltage 828 can be generated at the collector of the PNPbipolar transistor 822 (i.e., at the junction node).

It should be appreciated that the voltage source 804, the resistor 820,and the PNP bipolar transistor 822 form a current source operable toprovide a fixed current, I3. It should be appreciated that the voltagesource 812, the magnetoresistance element 826, and the NPN bipolartransistor 824 form a variable current sink operable to provide avariable current, I4. The variable current, I4, varies in accordancewith a variable resistance of the magnetoresistance element 826, whichvaries in accordance with a sensed magnetic field. Thus, the outputvoltage 828 is generated according to the following:

Vout2=Vb+[(I3−I4)×Zload2]

I3=(V1−Vbe)/R2

I4=(V2−Vbe)/B

I3−I4=(V1−Vbe)/R2−(V2−Vbe)/B

Vout2=Vb+[[(V1−Vbe)/R2−(V2−Vbe)/B]×Zload2]  (9)

where:

-   -   Zload2=impedance of load 830    -   Vout2=voltage 828    -   V1=voltage of voltage source 804    -   V2=voltage of voltage source 812    -   R2=resistance of resistor 820    -   B=resistance of the magnetoresistance element 826    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 822 and of        NPN bipolar transistor 824=approx. 0.7 volts

In the electronic circuit 800, it should be appreciated that the samecurrent, I4, flows through the NPN bipolar transistor 824 and throughthe magnetoresistance element 826.

For the electronic circuit 800, the output voltages 816, 828 can betaken individually (i.e., each can be a single ended signal). In otherembodiments, the electronic circuit 800 provides a differential signal,Vdiff=voltage 816−voltage 828=Vout1−Vout2.

It should be understood that the loads 818, 830 can be made to have highimpedances to achieve single ended gains not obtained with theelectronic circuits of FIGS. 1-4 described above. Furthermore, the abovedescribed differential signal has an amplitude that is double theamplitude of the single ended signals.

Referring now to FIG. 9, a magnetic field sensor 900 can include asubstrate 902 having a surface 902 a, which is one of two parallel majorsurfaces of the substrate 902.

Two magnetoresistance elements 904, 906 (also referred to herein asmagnetoresistance elements A and B) can be disposed upon the surface 902a along an axis 908. The two magnetoresistance elements 904, 906 (A, B)can be part of or coupled to an electronic circuit 910, which is alsodisposed upon or within the surface 902 a of the substrate 902. The twomagnetoresistance elements 904, 906 (A, B) can be the same as or similarto the magnetic field sensing elements 706, 714 of FIG. 7 and the twomagnetoresistance element 806, 812 of FIG. 3-8. The designations A, Bcan also be found in FIGS. 7 and 8 to represent resistance values.

Magnetoresistance elements, e.g., 904, 906 (A, B), are shown in allembodiments herein to be in the form of so-called “yokes,” which have aC-shape (or a reverse C-shape). In some embodiments, the yokes can havelongest yoke axes substantially perpendicular to the axis 908.Advantages of yoke shapes are known. It will be understood that othermagnetoresistance elements used in embodiments herein can have othershapes, for example, lines, polylines, or rectangles.

Maximum response axes of the magnetoresistance elements 904, 906 (A, B)can be parallel to and along the axis 908 and in the same direction. Itshould be understood that the magnetoresistance elements 904, 906 (A, B)having maximum response axes parallel to the axis 908 are alsoresponsive to magnetic fields at other angles in the plane of thesubstrate 902 (and also out of the plane of the substrate 902). Thedegree to which the magnetoresistance elements 904, 906 (A, B) areresponsive to magnetic fields at other angles not parallel to the axis908 (and not perpendicular to the longest yoke axes) is determined by amagnitude of a geometric projection of the magnetic field at the otherangle onto the axis 908. Thus, the term “projected magnetic field” isused below to describe this projection.

In some other embodiments, where the yoke shapes of themagnetoresistance elements 904, 906 may be rotated so that the longestyokes axes are not perpendicular to the axis 908, the degree to whichthe magnetoresistance elements 904, 906 (A, B) are responsive tomagnetic fields at other angles not parallel to the axis 908 isdetermined by a magnitude of a geometric projection of the magneticfield at the other angle onto an axis that is perpendicular to thelongest axes of the yoke shapes. This is also referred to herein as aprojected magnetic field.

The magnetic field sensor 900 is responsive to movement of aferromagnetic target object 912 having features, e.g., 912 a, with width914. For back-biased arrangements in which the magnetic field sensor 900also includes a magnet (not shown), the ferromagnetic target 912 objectcan be, for example, a gear having gear teeth, in which case, thefeature 912 a of the gear can be one of a plurality of gear teeth or oneof a plurality of gear valleys. In other arrangements, the ferromagnetictarget object 912 can be a multi-pole ring magnet having alternatingnorth and south poles, in which case, the feature 912 a can be one of aplurality of magnetic poles, for example, a north pole or a south pole.

In some embodiments, the two magnetoresistance elements 904, 906 (A, B)have a separation 916 between about one half and about one and one halfof the width 914 of the target feature 912 a, for example, a gear toothof a ferromagnetic gear or a magnetic domain of a ferromagnetic ringmagnet. In some other embodiments, the two magnetoresistance elements904, 906 (A, B) have a separation 916 between about one half and abouttwice the width 914 of the target feature 912 a. However, in otherembodiments, the separation 916 is much smaller than half of the width914, for example, one one hundredth of the width 914, or larger thantwice the width 914.

In some embodiments, the separation 916 is about equal to the width 914of the target feature 912 a, for example, a gear tooth of aferromagnetic gear or a magnetic domain of a ferromagnetic ring magnet.

In operation, the two magnetoresistance elements 904, 906 (A, B) cangenerate two output signals. FIGS. 7 and 8 above are representative ofways in which the two magnetic field sensing elements 904, 906 cangenerate two output signals. In FIGS. 7 and 8, the designation A and Bare indicative of resistances and are also indicative of physicalplacement in relation to FIG. 9.

Using as an example the target feature 912 a with a width 914 equal tothe spacing 916 between the two magnetoresistance elements 904, 906,when the target feature 912 a is centered about (i.e., between) the twomagnetoresistance elements 904, 906 (A, B), it can be shown that anymagnetoresistance element(s) (e.g., 904 (A)) on one side of a center ofthe target feature 912 a experience a projected magnetic field pointedin one direction along the axis 908, and any magnetoresistanceelement(s) (e.g., 906 (B)) on the other side of the center of the targetfeature 912 a experience a projected magnetic field pointed in the otherdirection.

Therefore, when the target feature 912 a is centered about the twomagnetoresistance elements 904, 906, any magnetoresistance element(s)(e.g., 904 (A)) on one side of the center of the target feature 912 achanges resistance in one direction, and any magnetoresistanceelement(s) (e.g., 906 (B)) on the other side of the center of the targetfeature 912 a changes resistance in the other direction.

In contrast, when an edge of the target feature 912 a is centered about(i.e., between) the two magnetoresistance elements 904, 906 (A, B), itcan be shown that the two magnetoresistance elements 904, 906 (A, B)experience projected magnetic fields pointed in the same direction alongthe axis 908. Thus, resistances of both of the two magnetoresistanceelements 904, 906 (A, B) change in the same direction.

In view of the above, it should be understood that the electroniccircuit 700 of FIG. 7 can operate as a so-called “edge detector,”generating a largest voltage 716 when the two magnetoresistance elements706, 714 are on opposite sides of an edge of the feature 912 a.Similarly, it should be understood that the electronic circuit 800 ofFIG. 8 can operate as a so-called “feature detector,” generating alargest differential signal Vout1−Vout2 when the two magnetoresistanceelements 806, 826 are on opposite sides of a center of the feature 912a.

As described above, while a magnet is not shown, it should be understoodthat in some embodiments, the magnetic field sensor 900 can include amagnet.

Referring now to FIG. 10, another example of an electronic circuit 1000can be used in another magnetic field sensor. The electronic circuit1000 can include a magnetoresistance element 1006 having first andsecond terminals, wherein the first terminal of the magnetoresistanceelement 1006 is coupled to receive a voltage 1002 and the secondterminal of the magnetoresistance element 1006 is coupled to an emitterof a PNP bipolar transistor 1008.

The electronic circuit 1000 can include a voltage source 1004 havingfirst and second terminals, wherein the first terminal of the voltagesource 1004 is coupled to receive the voltage 1002 and the secondterminal of the voltage source 1004 is coupled to a base of the PNPbipolar transistor 1008.

The electronic circuit 1000 can include another magnetoresistanceelement 1014 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1014 is coupled to an emitterof an NPN bipolar transistor 1010 and the second terminal of themagnetoresistance element 1014 is coupled to a voltage reference, forexample, a ground voltage.

The electronic circuit 1000 can include another voltage source 1012having first and second terminals, wherein the first terminal of thevoltage source 1012 is coupled a base of the NPN bipolar transistor 1010and the second terminal of the voltage source 1012 is coupled to thesecond terminal of the magnetoresistancc element 1014.

A collector of the PNP bipolar transistor 1008 can be coupled to acollector of the NPN bipolar transistor 1010 at a junction node.

A load 1018, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 1018.

The load 1018 is labeled Zload1. The nomenclature, Zload1, used here andin figures below is not intended to limit the load 1018 or loadsdiscussed below to one or more passive electronic components. Instead,the load 1018 and loads discussed below can be comprised of passiveelectronic components, active electronic components, or both.

An output voltage 1016 can be generated at the collector of the PNPbipolar transistor 1008 (i.e., at the junction node).

It should be appreciated that the voltage source 1004, themagnetoresistance element 1006, and the PNP bipolar transistor 1008 forma variable current source operable to provide a variable current, I1.The variable current, I1, varies in accordance with a variableresistance of the magnetoresistance element 1006, which varies inaccordance with a sensed magnetic field.

It should be appreciated that the voltage source 1012, themagnetoresistance element 1014, and the NPN bipolar transistor 1010 forma variable current sink operable to provide a variable current, I2. Thevariable current, I2, varies in accordance with a variable resistance ofthe magnetoresistance element 1014, which varies in accordance with asensed magnetic field. Thus, the output voltage 1016 is generatedaccording to the following:

Vout1=Vb+[(I1−I2)×Zload1]

I1=(V1−Vbe)/A

I2=(V2−Vbe)/D

I1−I2=(V1−Vbe)/A−(V2−Vbe)/D

Vout1=Vb+[[(V1−Vbe)/A−(V2−Vbe)/D]×Zload1]  (10)

where:

-   -   Zload1=impedance of load 1018    -   Vout1=voltage 1016    -   V1=voltage of voltage source 1004    -   V2=voltage of current mirror reference leg 1102    -   D=resistance of magnetoresistance element 1014    -   A=resistance of the magnetoresistance element 1006    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 1008 and of        NPN bipolar transistor 1010=approx. 0.7 volts

In the electronic circuit 1000, it should be appreciated that the samecurrent, I1, flows through the PNP bipolar transistor 1008 and throughthe magnetoresistance element 1006. Also, the same current, I2,(different than I1) flows through the NPN bipolar transistor 1010 andthrough the magnetoresistance element 1014.

The electronic circuit 1000 can also include a magnetoresistance element1020 having first and second terminals, wherein the first terminal ofthe magnetoresistance element 1020 is coupled to receive the voltage1002 and the second terminal of the magnetoresistance element 1020 iscoupled to an emitter of a PNP bipolar transistor 1022.

The second terminal of the voltage source 1004 can be coupled to a baseof the PNP bipolar transistor 1022.

The electronic circuit 1000 can include another magnetoresistanceelement 1026 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1026 is coupled to an emitterof an NPN bipolar transistor 1024 and the second terminal of themagnetoresistance element 1026 is coupled to a voltage reference, forexample, a ground voltage.

The first terminal of the voltage source 1012 is coupled a base of theNPN bipolar transistor 1024.

A collector of the PNP bipolar transistor 1022 can be coupled to acollector of the NPN bipolar transistor 1024 at a junction node.

A load 1030, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 1030.

The load 1030 is labeled Zload2. The nomenclature, Zload2, used here andin figures below is not intended to limit the load 1030 or loadsdiscussed below to one or more passive electronic components. Instead,the load 1030 and loads discussed below can be comprised of passiveelectronic components, active electronic components, or both.

An output voltage 1028 can be generated at the collector of the PNPbipolar transistor 1022 (i.e., at the junction node).

It should be appreciated that the voltage source 1004, themagnetoresistance element 1020, and the PNP bipolar transistor 1022 forma current source operable to provide a variable current, I3. Thevariable current, I3, varies in accordance with a variable resistance ofthe magnetoresistance element 1020, which varies in accordance with asensed magnetic field.

It should be appreciated that the voltage source 1012, themagnetoresistance element 1026, and the NPN bipolar transistor 1024 forma variable current sink operable to provide a variable current, I4. Thevariable current, I4, varies in accordance with a variable resistance ofthe magnetoresistance element 1026, which varies in accordance with asensed magnetic field. Thus, the output voltage 1028 is generatedaccording to the following:

Vout2=Vb+[(I3−I4)×Zload2]

I3=(V1−Vbe)/C

I4=(V2−Vbe)/B

I3−I4=(V1−Vbe)/C−(V2−Vbe)/B

Vout2=Vb+[[(V1−Vbe)/C−(V2−Vbe)/B]×Zload2]  (11)

where:

-   -   Zload2==impedance of load 1030    -   Vout2=voltage 1028    -   V1=voltage of voltage source 1004    -   V2=voltage of voltage source 1012    -   C=resistance of magnetoresistance element 1020    -   B=resistance of the magnetoresistance element 1026    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 1022 and of        NPN bipolar transistor 1024=approx. 0.7 volts

In the electronic circuit 1000, it should be appreciated that the samecurrent, I3, (different than I1, I2) flows through the PNP bipolartransistor 1022 and through the magnetoresistance element 1020. Also,the same current, I4, (different than I1, I2, I3) flows through the NPNbipolar transistor 1024 and through the magnetoresistance element 1026.

For the electronic circuit 1000, the output voltages 1016, 1028 can betaken individually (i.e., each can be a single ended signal). In otherembodiments, the electronic circuit 1000 provides a differential signal,Vdiff=voltage 1016−voltage 1028=Vout1−Vout2.

It should be understood that the loads 1018, 1030 can be made to havehigh impedances to achieve single ended gains not obtained with theelectronic circuits of FIGS. 1-4 described above. Furthermore, the abovedescribed differential signal has an amplitude that is double theamplitude of the single ended signals.

Referring now to FIG. 11, in which like elements of FIG. 10 are shownhaving like reference designations, in an electronic circuit 1100, thevoltage source 1012 of FIG. 10 is replaced with a circuit portion 1102,which will be recognized to be a reference leg of a current mirror. Thecircuit portion 1102 can include a current source 1104 having an outputnode. A collector of an NPN bipolar transistor 1106 can be coupled tothe current source. A base of the NPN bipolar transistor 1106 can becoupled to the collector of the NPN bipolar transistor 1106, such thatthe NPN bipolar transistor operates merely as a diode. A resistor 1180having first and second terminals can be coupled such that the firstterminal of the resistor is coupled to an emitter of the NPN bipolartransistor 1106 and the second terminal of the resistor 1108 is coupledto a reference voltage, for example, a ground voltage. The base or theNPN bipolar transistor 1106 is coupled to the bases of the NPN bipolartransistors 1010, 1024,

The electronic circuit 1100 operates in substantially the same way asthe electronic circuit 1000 of FIG. 10, and has the same operatingequations.

Referring now to FIG. 12, in which like elements of FIGS. 10 and 11 areshown having like reference designations, in an electronic circuit 1200,the voltage source 1004 of FIGS. 10 and 11 is replaced with a circuitportion 1202, which operates as a common mode voltage detector. Thecircuit portion 1202 can include a common mode voltage detector 1204coupled to receive the two output voltages 1016, 1028 and operable togenerate a common mode detection signal 1204 a indicative of a commonmode voltage of the output voltages 1016, 1028. A voltage buffer orlevel translator 1206 can be coupled to receive the common modedetection signal 1204 a and operable to generate a signal coupled to thebases of the PNP bipolar transistors 1008, 1022.

In operation, if a common voltage of a differential signal Vout1−Vout2is not at a desired operating point, the common mode voltage detector1204 can detect the error condition and adjust the current flowingthrough the two PNP bipolar transistors 1008, 1022 to remove the errorcondition.

The electronic circuit 1200 operates in substantially the same way asthe electronic circuit 1000 of FIG. 10 and the electronic circuit 1100of FIG. 1, and has the same operating equations.

Referring now to FIG. 13, in which like elements of FIG. 9 are shownhaving like, reference designations, a magnetic field sensor 1300 caninclude a substrate 1302 having a surface 1302 a, which is one of twoparallel major surfaces of the substrate 1302.

Four magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) canbe disposed upon the surface 1302 a along an axis 1314. The fourmagnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can bepart of or coupled to an electronic circuit 1312, which is also disposedupon or within the surface 1302 a of the substrate 1302. The fourmagnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) can bethe same as or similar to the magnetic field sensing elements 1006,1026, 1020, 1014, respectively, of FIGS. 10 and 11.

Maximum response axes of the four magnetoresistance elements 1304, 1306,1308, 1310 (A, B, C, D) can be parallel to and along an axis 1314, andin the same direction. Angles of magnetic fields are discussed above inconjunction with FIG. 9.

The magnetic field sensor 1300 is responsive to movement of theferromagnetic target object 912.

In some embodiments, the four magnetoresistance elements 1304, 1306,1308, 1310 (A, B, C, D) are disposed along the axis 1314 proximate tothe ferromagnetic target object 912.

In some embodiments, the two magnetoresistance elements 1304, 1308 (A,C) have a separation 1320 between about one half and about one and onehalf of the width 914 of the target feature 912 a, for example, a geartooth of a ferromagnetic gear or a magnetic domain of a ferromagneticring magnet. In some other embodiments, the two magnetoresistanceelements 1304, 1308 (A, C) have a separation 1320 between about one halfand about twice the width 914 of the target feature 912 a. However, inother embodiments, the separation 1320 is much smaller than half of thewidth 914, for example, one one hundredth of the width 914 or largerthan twice the width 914.

In some embodiments used in examples below, the separation 1320 is aboutequal to the width 914 of the target feature 912 a.

Similarly, in some embodiments, the two magnetoresistance elements 1306,1310 (B, D) have a separation 1322 between about one half and about oneand one half of the width 914 of the target feature 912 a, for example,a gear tooth of a ferromagnetic gear or a magnetic domain of aferromagnetic ring magnet. In some embodiments, the twomagnetoresistance elements 1306, 1310 (B, D) have a separation 1322between about one half and about twice the width 914 of the targetfeature 912 a. However, in other embodiments, the separation 1322 ismuch smaller than half of the width 914, for example, one one hundredthof the width 914 or larger than twice the width 914.

In some embodiments used in examples below, the separation 1322 is aboutequal to the width 914 of the target feature 912 a.

In some other embodiments, the two magnetoresistance elements 1304, 1306(A, B) have a separation 1324 between about one half and about one andone half of the width 914 of the target feature 912 a. In some otherembodiments, the two magnetoresistance elements 1304, 1306 (A, B) have aseparation 1324 between about one half and about twice the width 914 ofthe target feature 912 a. However, in other embodiments, the separation1324 is much smaller than half of the width 914, for example, one onehundredth of the width 914 or larger than twice the width 914.

In some embodiments used in examples below, the separation 1324 is aboutequal to the width 914 of the target feature 912 a.

Similarly, in some other embodiments, the two magnetoresistance elements1308, 1310 (C, D) have a separation 1326 between about one half andabout one and one half of the width 914 of the target feature 912 a. Insome other embodiments, the two magnetoresistance elements 1308, 1310(C, D) have a separation 1326 between about one half and twice the width914 of the target feature 912 a. However, in other embodiments, theseparation 1326 is much smaller than half of the width 914, for example,one one hundredth of the width 914 or larger than twice the width 914.

In some embodiments used in examples below, the separation 1326 is aboutequal to the width 914 of the target feature 912 a.

In operation, the four magnetoresistance elements 1304, 1306, 1308, 1310(A, B, C, D) can generate at least two output signals. FIGS. 10, 11, and12 above are representative of ways in which the four magnetoresistanceelements 1304, 1306, 1308, 1310 (A, B, C, D) can generate at least twooutput signals. In FIGS. 10, 11, and 12, the designation A, B, C, and Dare indicative of resistances and are also indicative of physicalplacement in relation to FIG. 13.

Using as an example the target feature 912 a with a width 914 equal tothe spacings 1320, 1322, when the target feature 912 a is centered about(i.e., between) the four magnetoresistance elements 1304, 1306, 1308,1310 (A, B, C, D), it can be shown that any magnetoresistance element(s)(e.g., 1304, 1306 (A, B)) on one side of a center of the target feature912 a experiences a projected magnetic field pointed in one directionalong the axis 1314, and any magnetoresistance element(s) (e.g., 1308,1310 (C, D)) on the other side of the center of the target feature 912 aexperiences a projected magnetic field pointed in the other direction.

Therefore, when the target feature 912 a is centered about fourmagnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D), anymagnetoresistance element(s) (e.g., 1304, 1306 (A, B)) on one side ofthe center of the target feature 912 a change resistance in onedirection, and any magnetoresistance element(s) (e.g., 1308, 1310 (C,D)) on the other side of the center of the target feature 912 a changeresistance in the other direction.

In contrast, when an edge of the target feature 912 a is centered about(i.e., between) the four magnetoresistance elements 1304, 1306, 1308,1310 (A, B, C, D), it can be shown that the two magnetoresistanceelements 1304, 1310 (A, D) experience projected magnetic fields pointedin the same direction along the axis 1314. Thus, resistance of both ofthe two magnetoresistance elements 1304, 1310 change in the samedirection.

At the same time, when an edge of the target feature 912 a is centered,the two magnetoresistance elements 1306, 1308 (B, C) experienceprojected magnetic fields pointed in the same direction along the axis1314, but opposite in direction from the projected magnetic fieldsexperienced by the two magnetoresistance elements 1304, 1310 (A, D).Thus, resistance of both of the two magnetoresistance elements 1306,1308 (B, C) change in the same direction but opposite to the resistancechange of the two magnetoresistance elements 1304, 1310 (A, D).

While a particular example of the spacings 1320, 1322 relative to thewidth 914 of the target feature 912 a is given above, it should beappreciated that for other relative dimensions, magnetic fields at thefour magnetoresistance elements 1304, 1306, 1308, 1310 (A, B, C, D) maynot be exactly as described above and some resistance changes may be inother directions.

In view of the above, it should be understood that the electroniccircuits 1000, 1100, 1200 of FIGS. 10, 11, 12 can operate as a featuredetectors, generating a largest differential voltage Vout1−Vout2 whenthe four magnetoresistance elements 1004 (A), 1026 (B), 1020 (C), 1014(D) of FIGS. 10, 11, 12 are arranged as shown in FIG. 13 by designationsA-D, arranged relative to a center of the target feature 912 a.

While a magnet is not shown, it should be understood that in someembodiments, the magnetic field sensor 1400 can include a magnet.

Referring now to FIG. 14, another example of an electronic circuit 1400can be used in another magnetic field sensor. The electronic circuit1400 can include a magnetoresistance element 1404 having first andsecond terminals, wherein the first terminal of the magnetoresistanceelement 1404 is coupled to receive a voltage 1402 and the secondterminal of the magnetoresistance element 1404 is coupled to an emitterof a PNP bipolar transistor 1406.

The electronic circuit 1400 can include a voltage source in the form ofa common mode voltage detector circuit 1435 coupled to the base of thePNP bipolar transistor 1406.

The electronic circuit 1400 can include another magnetoresistanceelement 1410 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1410 is coupled to an emitterof an NPN bipolar transistor 1408 and the second terminal of themagnetoresistance element 1410 is coupled to a voltage reference, forexample, a ground voltage.

The electronic circuit 1400 can include a voltage source in the form ofa current mirror reference leg 1428 coupled to the base of the NPNbipolar transistor 1408.

A collector of the PNP bipolar transistor 1406 can be coupled to acollector of the NPN bipolar transistor 1408 at a junction node.

A load 1414, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 1414.

The load 1414 is labeled Z1. The nomenclature, Z1, is not intended tolimit the load 1414 to one or more passive electronic components.Instead, the load 1414 can be comprised of passive electroniccomponents, active electronic components, or both.

An output voltage 1412 can be generated at the collector of the PNPbipolar transistor 1406 (i.e., at the junction node).

The output voltage 1412 is generated according to the following:

Vout1=Vb+[(I1−I2)×Z1]

I1=(V1−Vbe)/A1

I2=(V2−Vbe)/C2

I1−I2=(V1−Vbe)/A1−(V2−Vbe)/C2

Vout1=Vb+[[(V1−Vbe)/A1−(V2−Vbe)/C2]×Z1]  (12)

where:

-   -   Z1=impedance of load 1414    -   Vout1=voltage 1412    -   V1=voltage of common mode voltage detector circuit 1435    -   V2=voltage of current mirror reference let 1428    -   C2=resistance of magnetoresistance element 1410    -   A1=resistance of the magnetoresistance element 1404    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 1406 and of        NPN bipolar transistor 1408=approx. 0.7 volts

The electronic circuit 1400 can also include a magnetoresistance element1416 having first and second terminals, wherein the first terminal ofthe magnetoresistance element 1416 is coupled to receive the voltage1402 and the second terminal of the magnetoresistance element 1416 iscoupled to an emitter of a PNP bipolar transistor 1418.

The common mode voltage detector circuit 1435 can be coupled to a baseof the PNP bipolar transistor 1418.

The electronic circuit 1400 can include another magnetoresistanceelement 1422 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1422 is coupled to an emitterof an NPN bipolar transistor 1420 and the second terminal of themagnetoresistance element 1422 is coupled to a voltage reference, forexample, a ground voltage.

The current mirror reference leg 1428 is coupled to a base of the NPNbipolar transistor 1420.

A collector of the PNP bipolar transistor 1418 can be coupled to acollector of the NPN bipolar transistor 1420 at a junction node.

A load 1426, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 1426

The load 1426 is labeled Z2. The nomenclature, Z2, is not intended tolimit the load 1426 to one or more passive electronic components.Instead, the load 1426 can be comprised of passive electroniccomponents, active electronic components, or both.

An output voltage 1424 can be generated at the collector of the PNPbipolar transistor 1418 (i.e., at the junction node).

The output voltage 1424 is generated according to the following:

Vout2=Vb+[(I3−I4)×Z2]

I3=(V1−Vbe)/C1

I4=(V2−Vbe)/A2

I3−I4=(V1−Vbe)/C1−(V2−Vbe)/A2

Vout2=Vb+[[(V1−Vbe)/C1−(V2-Vbe)/A2]×Z2]  (13)

where:

-   -   Z2=impedance of load 1426    -   Vout2=voltage 1424    -   V1=voltage of common mode voltage detector circuit 1435    -   V2=voltage of current mirror reference leg 1428    -   C1=resistance of resistor 1416    -   A2=resistance of the magnetoresistance element 1422    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 1418 and of        NPN bipolar transistor 1024=approx. 0.7 volts

In the electronic circuit 1400, it should be appreciated that the samecurrent, I3, (different than I1, I2) flows through the PNP bipolartransistor 1418 and through the magnetoresistance element 1416. Also,the same current, I4, (different than I1, I2, I3) flows through the NPNbipolar transistor 1024 and through the magnetoresistance element 1422.

For the electronic circuit 1400, the output voltages 1412, 1424 can betaken individually (i.e. single ended signals). In other embodiments,the electronic circuit 1400 provides a differential signal,Vdiff=voltage 1412−voltage 1424=Vout1−Vout2.

It should be understood that the loads 1414, 1426 can be made to havehigh impedances to achieve single ended gains not obtained with theelectronic circuits of FIGS. 1-4 described above. Furthermore, the abovedescribed differential signal has an amplitude that is double theamplitude of the single ended signals.

The electronic circuit 1400 can also include a magnetoresistance element1440 having first and second terminals, wherein the first terminal ofthe magnetoresistance element 1440 is coupled to receive a voltage 1402and the second terminal of the magnetoresistance element 1440 is coupledto an emitter of a PNP bipolar transistor 1442.

The electronic circuit 1400 can include a common mode voltage detectorcircuit 1471 coupled to a base of the PNP bipolar transistor 1442.

The electronic circuit 1400 can include another magnetoresistanceelement 1446 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1446 is coupled to an emitterof an NPN bipolar transistor 1444 and the second terminal of themagnetoresistance element 1446 is coupled to a voltage reference, forexample, a ground voltage.

The electronic circuit 1400 can include a current mirror reference leg1464 coupled a base of the NPN bipolar transistor 1444.

A collector of the PNP bipolar transistor 1442 can be coupled to acollector of the NPN bipolar transistor 1444 at a junction node.

A load 1450, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 1450.

The load 1450 is labeled Z3. The nomenclature, Z3, is not intended tolimit the load 1450 to one or more passive electronic components.Instead, the load 1450 can be comprised of passive electroniccomponents, active electronic components, or both.

An output voltage 1448 can be generated at the collector of the PNPbipolar transistor 1442 (i.e., at the junction node).

The output voltage 1448 is generated according to the following:

Vout3=Vb+[(I5−I6)×Z3]

I5=(V3−Vbe)B1

I6=(V4−Vbe)/D2

I5−I6=(V3−Vbe)/B1−(V4-Vbe)/D2

Vout3=Vb+[[(V3−Vbe)/B1−(V4−Vbe)/D2]×Z3]  (14)

where:

-   -   Z3=impedance of load 1450    -   Vout3=voltage 1448    -   V3=voltage of common mode voltage detector circuit 1471    -   V4=voltage of current mirror reference leg 1464    -   D2=resistance of magnetoresistance element 1446    -   B1=resistance of the magnetoresistance element 1440    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 1442 and of        NPN bipolar transistor 1444=approx. 0.7 volts

The electronic circuit 1400 can also include a magnetoresistance element1452 having first and second terminals, wherein the first terminal ofthe magnetoresistance element 1452 is coupled to receive the voltage1402 and the second terminal of the magnetoresistance element 1452 iscoupled to an emitter of a PNP bipolar transistor 1454.

The common mode voltage detector circuit 1471 can be coupled to a baseof the PNP bipolar transistor 1454.

The electronic circuit 1400 can include another magnetoresistanceelement 1458 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1458 is coupled to an emitterof an NPN bipolar transistor 1456 and the second terminal of themagnetoresistance element 1458 is coupled to a voltage reference, forexample, a ground voltage.

The current mirror reference leg 1464 is coupled to a base of the NPNbipolar transistor 1456.

A collector of the PNP bipolar transistor 1454 can be coupled to acollector of the NPN bipolar transistor 1456 at a junction node.

A load 1462, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 1462

The load 1462 is labeled Z4. The nomenclature, Z4, is not intended tolimit the load 1462 to one or more passive electronic components.Instead, the load 1462 can be comprised of passive electroniccomponents, active electronic components, or both.

An output voltage 1460 can be generated at the collector of the PNPbipolar transistor 1454 (i.e., at the junction node).

The output voltage 1460 is generated according to the following:

Vout4=Vb+[(I7−I8)×Z4]

I7=(V3−Vbe)/D1

I8=(V4−Vbe)/B2

I7−I8=(V3−Vbe)/D1−(V4−Vbe)/B2

Vout4=Vb+[[(V3−Vbe)/D1−(V4−Vbe)/B2]×Z4]  (15)

where:

-   -   Z4=impedance of load 1462    -   Vout4=voltage 1460    -   V3=voltage of common mode voltage detector circuit 1471    -   V4=voltage of current mirror reference leg 1464    -   D1=resistance of magnetoresistance element 1452    -   B2=resistance of the magnetoresistance element 1458    -   Vb=bias voltage    -   Vbe=base emitter voltage of PNP bipolar transistor 1454 and of        NPN bipolar transistor 1456=approx. 0.7 volts

For the electronic circuit 1400, the output voltages 1448, 1460 can betaken individually (i.e. single ended signals). In other embodiments,the electronic circuit 1400 provides a differential signal,Vdiff=voltage 1448−voltage 1460=Vout3−Vout4.

It should be understood that the loads 1450, 1462 can be made to havehigh impedances to achieve single ended gains not obtained with theelectronic circuits of FIGS. 1-4 described above. Furthermore, the abovedescribed differential signal has an amplitude that is double theamplitude of the single ended signals.

As described above, for the electronic circuit 1400, the output voltages1412, 1424, 1448, 1460 can be taken individually (i.e., single ended).However, in other embodiments, the output voltages 1412, 1424, 1448,1460 can be combined in any way, for example, resulting in twodifferential signals.

Referring now to FIG. 15, in which like elements of FIG. 9 are shownhaving like reference designations, a magnetic field sensor 1500 caninclude a substrate 1502 having a surface 1502 a, which is one of twoparallel major surfaces of the substrate 1502.

The eight magnetoresistance elements 1504 a, 1504 b, 1506 a, 1506 b,1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2, D1, D2) can bedisposed upon the surface 1502 a along an axis 1514. The eightmagnetoresistance elements 1504 a, 1504 b, 1506 a, 1506 b, 1508 a, 1508b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2, D1, D2) can be part of orcoupled to an electronic circuit 1512, which is also disposed upon orwithin the surface 1502 a of the substrate 1502. The eightmagnetoresistance elements 1504 a, 1504 b, 1506 a, 1506 b, 1508 a, 1508b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2, D1, D2) can be the same as orsimilar to the eight magnetoresistance elements of FIG. 14.

Maximum response axes of the eight magnetoresistance elements 1504 a,1504 b, 1506 a, 1506 b, 1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2,C1, C2, D1, D2) can be parallel to and along an axis 1514, and in thesame direction. Angles of magnetic fields are discussed above inconjunction with FIG. 9.

The magnetic field sensor 1500 is responsive to movement of theferromagnetic target object 912.

In some embodiments, the eight magnetoresistance elements 1504 a, 1504b, 1506 a, 1506 b, 1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2, C1,C2, D1, D2) are disposed along the axis 1514 proximate to theferromagnetic target object 912.

In some embodiments, the two magnetoresistance elements 1504 a, 1504 b(A1, A2) have a separation 1520 to the two magnetoresistance elements1508 a, 1508 b (C1, C2) between about one half and about one and onehalf of the width 914 of the target feature 912 a, for example, a geartooth of a ferromagnetic gear or a magnetic domain of a ferromagneticring magnet. In some embodiments, the two magnetoresistance elements1504 a, 1504 b (A1, A2) have a separation 1520 to the twomagnetoresistance elements 1508 a, 1508 b (C1, C2) between about onehalf and about twice the width 914 of the target feature 912 a. However,in other embodiments, the separation 1520 is much smaller than half ofthe width 914, for example, one one hundredth of the width 914, orlarger than twice the width 914.

In some embodiments used in examples below, the separation 1520 is aboutequal to the width 914 of the target feature 912 a.

Similarly, in some embodiments, the two magnetoresistance elements 1506a, 1506 b (B1, B2) have a separation 1522 to the two magnetoresistanceelements 1510 a, 1510 b (D1, D2) between about one half and about oneand one half of the width 914 of the target feature 912 a, for example,a gear tooth of a ferromagnetic gear or a magnetic domain of aferromagnetic ring magnet. In some embodiments, the twomagnetoresistance elements 1506 a, 1506 b (B1, B2) have a separation1522 to the two magnetoresistance elements 1510 a, 1510 b (D1, D2)between about one half and about twice the width 914 of the targetfeature 912 a. However, in other embodiments, the separation 1522 ismuch smaller than half of the width 914, for example, one one hundredthof the width 914, or larger than twice the width 914.

In some embodiments used in examples below, the separation 1522 is aboutequal to the width 914 of the target feature 912 a.

In some other embodiments, the two magnetoresistance elements 1504 a,1504 b (A1, A2) have a separation 1524 to the two magnetoresistanceelements 1506 a, 1506 b (B1, B2) between about one half and about oneand one half of the width 914 of the target feature 912 a.

In some other embodiments, the two magnetoresistance elements 1504 a,1504 b (A1, A2) have a separation 1524 to the two magnetoresistanceelements 1506 a, 1506 b (B1, B2) between about one half and twice thewidth 914 of the target feature 912 a. However, in other embodiments,the separation 1524 is much smaller than half of the width 914, forexample, one one hundredth of the width 914, or larger than twice thewidth 914.

In some embodiments used in examples below, the separation 1524 is aboutequal to the width 914 of the target feature 912 a.

Similarly, in some other embodiments, the two magnetoresistance elements1508 a, 1508 b (C1, C2) have a separation 1526 to the twomagnetoresistance elements 1510 a, 1510 b (D1, D2) between about onehalf and about one and one half of the width 914 of the target feature912 a. In some other embodiments, the two magnetoresistance elements1508 a, 1508 b (C1, C2) have a separation 1526 to the twomagnetoresistance elements 1510 a, 1510 b (D1, D2) between about twicethe width 914 of the target feature 912 a. However, in otherembodiments, the separation 1526 is much smaller than half of the width914, for example, one one hundredth of the width 914, or larger thantwice the width 914.

In some embodiments used in examples below, the separation 1526 is aboutequal to the width 914 of the target feature 912 a.

In operation, the eight magnetoresistance elements 1504 a, 1504 b, 1506a, 1506 b, 1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2, D1,D2) can generate at least two output signals. FIG. 14 is representativeof ways in which the eight magnetoresistance elements 1504 a, 1504 b,1506 a, 1506 b, 1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2,D1, D2) can generate at least two output signals. In FIG. 14 thedesignations A1, A2, B1, B2, C1, C2, D1, D2 are indicative ofresistances and are also indicative of physical placement in relation toFIG. 15.

Using as an example the target feature 912 a with a width 914 equal tothe spacings 1520, 1522, when the target feature 912 a is centered about(i.e., between) the eight magnetoresistance elements 1504 a, 1504 b,1506 a, 1506 b, 1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2,D1, D2), it can be shown that any magnetoresistance element(s) (e.g.,1504 a, 1504 b, 1506 a, 1506 b (A1, A2, B1, B2) on one side of a centerof the target feature 912 a experiences a projected magnetic fieldpointed in one direction along the axis 1514, and any magnetoresistanceelement(s) (e.g., 1508 a, 1508 b, 1510 a, 1510 b (C1, C2, D1, D1)) onthe other side of the center of the target feature 912 a experiences aprojected magnetic field pointed in the other direction.

Therefore, when the target feature 912 a is centered about eightmagnetoresistance elements 1504 a, 1504 b, 1506 a, 1506 b, 1508 a, 1508b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2, D1, D2), anymagnetoresistance element(s) (e.g., 1504 a, 1504 b, 1506 a, 1506 b (A1,A2, B1, B2)) on one side of the center of the target feature 912 achanges resistance in one direction, and any magnetoresistanceelement(s) (e.g., 1508 a, 1508 b, 1510 a, 1510 b (C1, C2, D1, D2)) onthe other side of the center of the target feature 912 a changesresistance in the other direction.

In contrast, when an edge of the target feature 912 a is centered about(i.e., between) the eight magnetoresistance elements 1504 a, 1504 b,1506 a, 1506 b, 1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2,D1, D2), it can be shown that the four magnetoresistance elements 1504a, 1504 b, 1510 a, 1510 b (A1, A2, D1, D2) experience projected magneticfields pointed in the same direction along the axis 1514. Thus,resistances the four magnetoresistance elements 1504 a, 1504 b, 1510 a,1510 b (A1, A2, D1, D2) change in the same direction.

At the same time, when an edge of the target feature 912 a is centered,the four magnetoresistance elements 1506 a, 1506 b, 1508 a, 1508 b (B1,B2, C1, C2) experience projected magnetic fields pointed in the samedirection along the axis 1514, but opposite in direction from theprojected magnetic fields experienced by the four magnetoresistanceelements 1504 a, 1504 b, 1510 a, 1510 b (A1, A2, D1, D2). Thus,resistance of four magnetoresistance elements 1506 a, 1506 b, 1508 a,1508 b (B1, B2, C1, C2) change in the same direction but opposite to theresistance change of the four magnetoresistance elements 1504 a, 1504 b,1510 a, 1510 b (A1, A2, D1, D2).

While a particular example of the spacings 1520, 1515 and 1524, 1526relative to the width 914 of the target feature 912 a is given above, itshould be appreciated that for other relative dimensions, magneticfields at the eight magnetoresistance elements 1504 a, 1504 b, 1506 a,1506 b, 1508 a, 1508 b, 1510 a, 1510 b (A1, A2, B1, B2, C1, C2, D1, D2)may not be exactly as described above and some resistance changes may bein other directions. However, it should be apparent how to modifyequations shown in figures below to accomplish both a feature signal andan edge signal.

While a magnet not shown, it should be understood that in someembodiments, the magnetic field sensor 1500 can include a magnet.

Referring now to FIG. 16, in which like elements of FIGS. 10, 11, and 12are shown having like reference designations, another example of anelectronic circuit 1600 can be used in another magnetic field sensor. Inthe electronic circuit 1600, a current mirror reference leg 1602 and acommon mode voltage detector circuit 1609 are exchanged in position andcouplings with the current mirror reference leg 1102 and a common modevoltage detector circuit 1202 of FIG. 12. Operation of the electroniccircuit 1600 is similar to operation of the electronic circuit 1200 ofFIG. 12.

It should be understood how a current mirror reference leg and a commonmode voltage detector circuit can be coupled in either way to all of theabove electronic circuits.

In FIG. 16, the designation A, B, C, and D are indicative of resistancesand are also indicative of physical placement in relation to FIG. 13.

Referring now to FIG. 17, another example of an electronic circuit 1700can be used in another magnetic field sensor. The electronic circuit1700 can include a magnetoresistance element 1704 having first andsecond terminals, wherein the first terminal of the magnetoresistanceelement 1704 is coupled to receive a voltage 1702 and the secondterminal of the magnetoresistance element 1704 is coupled to a source ofa P-channel field effect transistor 1706.

The electronic circuit 1700 can include a common mode voltage detectorcircuit 1727 coupled to a gate of the P-channel field effect transistor1706.

The electronic circuit 1700 can include another magnetoresistanceelement 1710 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1710 is coupled to a source ofan N-channel field effect transistor 1708 and the second terminal of themagnetoresistance element 1710 is coupled to a voltage reference, forexample, a ground voltage.

The electronic circuit 1700 can include a current mirror reference leg1732 coupled a gate of the N-channel field effect transistor 1708.

A drain of the P-channel field effect transistor 1706 can be coupled toa drain of the N-channel field effect transistor 1708 at a junctionnode.

A load 1714, which can be a resistive or a complex load, can be coupledbetween the junction node and t a bias voltage, Vb. Current can flowinto and/or out of the load 1714.

The load 1714 is labeled Zload1. The nomenclature, Zload1, is notintended to limit the load 1714 to one or more passive electroniccomponents. Instead, the load 1714 can be comprised of passiveelectronic components, active electronic components, or both.

An output voltage 1712 can be generated at the drain of the P-channelfield effect transistor 1706 (i.e., at the junction node).

It should be appreciated that the common mode voltage detector circuit1727, the magnetoresistance element 1704, and the P-channel field effecttransistor 1706 form a variable current source operable to provide avariable current, I1. The variable current, I1, varies in accordancewith a variable resistance of the magnetoresistance element 1704, whichvaries in accordance with a sensed magnetic field.

It should be appreciated that the current mirror reference leg 1732, themagnetoresistance element 1710, and the N-channel field effecttransistor 1708 form a variable current sink operable to provide avariable current, I2. The variable current, I2, varies in accordancewith a variable resistance of the magnetoresistance element 1710, whichvaries in accordance with a sensed magnetic field. Thus, the outputvoltage 1712 is generated according to the following:

Vout1=(I1−I2)×Zload1

Equations used to describe the voltage, Vout1, can be similar to theequations used to describe Vout1 in conjunction with FIG. 10 above,except that Vbe is replaced by Vgs, where Vgs=a gate source voltage ofthe field effect transistors (which can be different for P-channel andN-channel field defect transistors). A gate-source voltage can be nearone volt.

In the electronic circuit 1700, it should be appreciated that the samecurrent, I1 flows through the P-channel field effect transistor 1706 andthrough the magnetoresistance element 1704. Also, the same current, I2,flows through the N-channel field effect transistor 1708 and through themagnetoresistance element 1710.

The electronic circuit 1700 can also include a magnetoresistance element1716 having first and second terminals, wherein the first terminal ofthe magnetoresistance element 1716 is coupled to receive the voltage1702 and the second terminal of the magnetoresistance element 1716 iscoupled to a source of a P-channel field effect transistor 1718.

The common mode voltage detector circuit 1727 can be coupled to a gateof the P-channel field effect transistor 1718.

The electronic circuit 1700 can include another magnetoresistanceelement 1722 having first and second terminals, wherein the firstterminal of the magnetoresistance element 1722 is coupled to a source ofan N-channel field effect transistor 1720 and the second terminal of themagnetoresistance element 1722 is coupled to a voltage reference, forexample, a ground voltage.

The current mirror reference leg 1732 is coupled to a gate of theN-channel field effect transistor 1720.

A drain of the P-channel field effect transistor 1718 can be coupled toa drain of the N-channel field effect transistor 1720 at a junctionnode.

A load 1726, which can be a resistive or a complex load, can be coupledbetween the junction node and a bias voltage, Vb. Current can flow intoand/or out of the load 1726.

The load 1726 is labeled Zload2. The nomenclature, Zload2, is notintended to limit the load 1726 to one or more passive electroniccomponents. Instead, the load 1726 can be comprised of passiveelectronic components, active electronic components, or both.

An output voltage 1724 can be generated at the drain of the P-channelfield effect transistor 1718 (i.e., at the junction node).

It should be appreciated that the common mode voltage detector circuit1727, the magnetoresistance element 1716, and the P-channel field effecttransistor 1718 form a variable current source operable to provide avariable current, I3. The variable current, I3, varies in accordancewith a variable resistance of the magnetoresistance element 1716, whichvaries in accordance with a sensed magnetic field.

It should be appreciated that the current mirror reference leg 1732, themagnetoresistance element 1722, and the N-channel field effecttransistor 1720 form a variable current sink operable to provide avariable current, I4. The variable current, I4, varies in accordancewith a variable resistance of the magnetoresistance element 1722, whichvaries in accordance with a sensed magnetic field. Thus, the outputvoltage 1724 is generated according to the following:

Vout2=(I3−I4)×Zload2

Equations used to describe the voltage, Vout2, can be similar to theequations used to describe Vout2 in conjunction with FIG. 10 above,except that Vbe is replaced by Vgs where Vgs=a gate source voltage ofthe field effect transistors (which can be different for P-channel andN-channel field defect transistors). A gate-source voltage can be nearone volt.

In the electronic circuit 1700, it should be appreciated that the samecurrent, I1, flows through the P-channel field effect transistor 1706and through the magnetoresistance element 1704. Also, the same current,I2, flows through the N-channel field effect transistor 1708 and throughthe magnetoresistance element 1710.

In the electronic circuit 1700, it should be appreciated that the samecurrent, I3, flows through the P-channel field effect transistor 1718and through the magnetoresistance element 1716. Also, the same current,I4, flows through the N-channel field effect transistor 1720 and throughthe magnetoresistance element 1722.

For the electronic circuit 1700, the output voltages 1712, 1724 can betaken individually (i.e., single ended signals). In other embodiments,the electronic circuit 1700 provides a differential signal,Vdiff=voltage 1712−voltage 1724=Vout1−Vout2.

It should be understood that the loads 1714, 1726 can be made to havehigh impedances to achieve single ended gains not obtained with theelectronic circuits of FIGS. 1-4 described above. Furthermore, the abovedescribed differential signal has an amplitude that is double theamplitude of the single ended signals.

In FIG. 17, the designation A, B, C, and D are indicative of resistancesand are also indicative of physical placement in relation to FIG. 13.

It should be understood that all of the above electronic circuits canuse field effect transistors in place of bipolar junction transistors.

Some embodiments described above show two loads. Similar embodiments caninstead drive different ends of the same load. Some embodimentsdescribed above show four loads.

Similar embodiments can instead drive different ends of two loads. Otherload couplings are also possible.

While transistors are used in electronic circuits shown and describedherein, it should be understood that any electronic component or elementnow known or later discovered that has a control node to control acurrent passing between two current passing nodes can be used in placeof transistors.

Having described preferred embodiments, which serve to illustratevarious concepts, structures and techniques, which are the subject ofthis patent, it will now become apparent that other embodimentsincorporating these concepts, structures and techniques may be used.Accordingly, it is submitted that the scope of the patent should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the following claims.

Elements of embodiments described herein may be combined to form otherembodiments not specifically set forth above. Various elements, whichare described in the context of a single embodiment, may also beprovided separately or in any suitable subcombination. Other embodimentsnot specifically described herein are also within the scope of thefollowing claims.

What is claimed is:
 1. An electronic circuit, comprising, a firstmagnetoresistance element having first and second terminals; a firsttransistor having a control node, a first current passing node, and asecond current passing node; and a first voltage source having first andsecond nodes between which a first voltage is generated, wherein thefirst terminal of the first magnetoresistance element is coupled to thefirst current passing node of the first transistor, wherein the firstnode of the first voltage source is coupled to the control node of thefirst transistor and the second node of the first voltage source iscoupled to the second terminal of the first magnetoresistance element,wherein the electronic circuit is operable to generate a first currentsignal at the second current passing node of the first transistorrelated to a resistance value of the first magnetoresistance element. 2.The electronic circuit of claim 1, further comprising a resistor havingfirst and second terminals, the first terminal of the resistor coupledto the second current passing node of the first transistor, wherein theresistor is operable to pass the first current signal and convert thefirst current signal to a voltage signal at the second current passingnode of the first transistor.
 3. The electronic circuit of claim 1,wherein the first voltage source comprises a reference leg of a currentmirror circuit.
 4. The electronic circuit of claim 1, furthercomprising: a comparator coupled to the second current passing node ofthe first transistor for generating a two state output signal.
 5. Theelectronic circuit of claim 1, further comprising: a first resistorhaving first and second terminals; a second transistor having a controlnode, a first current passing node, and a second current passing node; asecond voltage source having first and second nodes between which asecond voltage is generated; and a first load coupled to the secondcurrent passing node of the first transistor, wherein the second currentpassing node of the first transistor is coupled to the second currentpassing node of the second transistor, wherein the first terminal of thefirst resistor is coupled to the first current passing node of thesecond transistor, wherein the first node of the second voltage sourceis coupled to the control node of the second transistor and the secondnode of the second voltage source is coupled to the second terminal ofthe first resistor, wherein the electronic circuit is operable togenerate a second current signal at the second current passing node ofthe second transistor related to a resistance value of the firstresistor, wherein a current passing through the first load is equal to adifference between the first current signal and the second currentsignal.
 6. The electronic circuit of claim 5, wherein the firsttransistor is an NPN bipolar transistor and the second transistor is abipolar PNP transistor.
 7. The electronic circuit of claim 5, whereinthe first transistor is a PNP bipolar transistor and the secondtransistor is an NPN bipolar transistor.
 8. The electronic circuit ofclaim 5, wherein the first voltage source comprises a reference leg of acurrent mirror circuit.
 9. The electronic circuit of claim 5, furthercomprising: a comparator coupled to the second current passing node ofthe first transistor for generating a two state output signal.
 10. Theelectronic circuit of claim 5, further comprising: a secondmagnetoresistance element having first and second terminals; a thirdtransistor having a control node, and first current passing node, and asecond current passing node; a third voltage source having first andsecond nodes between which a third voltage is generated, wherein thefirst terminal of the second magnetoresistance element is coupled to thefirst current passing node of the third transistor, wherein the firstnode of the third voltage source is coupled to the control node of thethird transistor and the second node of the third voltage source iscoupled to the second terminal of the second magnetoresistance element,wherein the electronic circuit is operable to generate a third currentsignal at the second current passing node of the third transistorrelated to a resistance value of the second magnetoresistance element,wherein the electronic circuit further comprises: a second resistorhaving first and second terminals; a fourth transistor having a controlnode, a first current passing node, and a second current passing node; afourth voltage source having first and second nodes between which afourth voltage is generated; and a second load coupled to the secondcurrent passing node of the third transistor, wherein the second currentpassing node of the third transistor is coupled to the second currentpassing node of the fourth transistor, wherein the first terminal of thesecond resistor is coupled to the first current passing node of thefourth transistor, wherein the first node of the fourth voltage sourceis coupled to the control node of the fourth transistor and the secondnode of the fourth voltage source is coupled to the second terminal ofthe second resistor, wherein the electronic circuit is operable togenerate a fourth current signal at the second current passing node ofthe fourth transistor related to a resistance value of the secondresistor, wherein a current passing through the second load is equal toa difference between the third current signal and the fourth currentsignal.
 11. The electronic circuit of claim 10, wherein the firstvoltage source and the third voltage source are a same first commonvoltage source.
 12. The electronic circuit of claim 11, wherein the samefirst common voltage source comprises a reference leg of a currentmirror circuit.
 13. The electronic circuit of claim 11, wherein thesecond voltage source and the fourth voltage source are a same secondcommon voltage source.
 14. The electronic circuit of claim 13, whereinthe same first common voltage source comprises a reference leg of acurrent mirror circuit and wherein the same second common voltage sourcecomprises a common mode voltage detector circuit coupled to the firstand second loads and configured to generate the first and third voltagesas the same common-mode-related voltage related to a common mode voltagebetween the first and second loads.
 15. The electronic circuit of claim10, wherein the second voltage source and the fourth voltage source area same common voltage source.
 16. The electronic circuit of claim 15,wherein the same common voltage source comprises a common mode voltagedetector circuit coupled to the first and second loads and configured togenerate the first and third voltages as the same common-mode-relatedvoltage related to a common mode voltage between the first and secondloads.
 17. The electronic circuit of claim 1, further comprising: asecond magnetoresistance element having first and second terminals; asecond transistor having a control node, a first current passing node,and a second current passing node; a second voltage source having firstand second nodes between which a second voltage is generated; and a loadcoupled to the second current passing node of the first transistor,wherein the second current passing node of the first transistor iscoupled to the second current passing node of the second transistor,wherein the first terminal of the second magnetoresistance element iscoupled to the first current passing node of the second transistor,wherein the first node of the second voltage source is coupled to thecontrol node of the second transistor and the second node of the secondvoltage source is coupled to the second terminal of the secondmagnetoresistance element, wherein the electronic circuit is operable togenerate a second current signal at the second current passing node ofthe second transistor related to a resistance value of the secondmagnetoresistance element, wherein a current passing through the load isequal to a difference between the first current signal and the secondcurrent signal.
 18. The electronic circuit of claim 17, wherein thefirst voltage source comprises a reference leg of a current mirrorcircuit.
 19. The electronic circuit of claim 17, further comprising: acomparator coupled to the second current passing node of the firsttransistor for generating a two state output signal.
 20. The electroniccircuit of claim 17, further comprising: a third magnetoresistanceelement having first and second terminals; a third transistor having acontrol node, and first current passing node, and a second currentpassing node; a third voltage source having first and second nodesbetween which a third voltage is generated, wherein the first terminalof the third magnetoresistance element is coupled to the first currentpassing node of the third transistor, wherein the first node of thethird voltage source is coupled to the control node of the thirdtransistor and the second node of the third voltage source is coupled tothe second terminal of the third magnetoresistance element, wherein theelectronic circuit is operable to generate a third current signal at thesecond current passing node of the third transistor related to aresistance value of the third magnetoresistance element, wherein theelectronic circuit further comprises: a fourth magnetoresistance elementhaving first and second terminals; a fourth transistor having a controlnode, a first current passing node, and a second current passing node; afourth voltage source having first and second nodes between which afourth voltage is generated; and a second load coupled to the secondcurrent passing node of the third transistor, wherein the second currentpassing node of the third transistor is coupled to the second currentpassing node of the fourth transistor, wherein the first terminal of thefourth magnetoresistance element is coupled to the first current passingnode of the fourth transistor, wherein the first node of the fourthvoltage source is coupled to the control node of the fourth transistorand the second node of the fourth voltage source is coupled to thesecond terminal of the fourth magnetoresistance element, wherein theelectronic circuit is operable to generate a fourth current signal atthe second current passing node of the fourth transistor related to aresistance value of the fourth magnetoresistance element, wherein acurrent passing through the second load is equal to a difference betweenthe third current signal and the fourth current signal.
 21. Theelectronic circuit of claim 20, wherein the first voltage source and thethird voltage source are a same first common voltage source.
 22. Theelectronic circuit of claim 21, wherein the same first common voltagesource comprises a reference leg of a current mirror circuit.
 23. Theelectronic circuit of claim 21, wherein the second voltage source andthe fourth voltage source are a same second common voltage source. 24.The electronic circuit of claim 23, wherein the same first commonvoltage source comprises a reference leg of a current mirror circuit andwherein the same second common voltage source comprises a common modevoltage detector circuit coupled to the first and second loads andconfigured to generate the first and third voltages as the samecommon-mode-related voltage related to a common mode voltage between thefirst and second loads.
 25. The electronic circuit of claim 20, whereinthe second voltage source and the fourth voltage source are a samecommon voltage source.
 26. The electronic circuit of claim 25, whereinthe same common voltage source comprises a common mode voltage detectorcircuit coupled to the first and second loads and configured to generatethe first and third voltages as the same common-mode-related voltagerelated to a common mode voltage between the first and second loads. 27.A magnetic field sensor, comprising: a substrate; and an electroniccircuit disposed upon the substrate, the electronic circuit comprising:a first magnetoresistance element having first and second terminals; afirst transistor having a control node, a first current passing node,and a second current passing node; and a first voltage source havingfirst and second nodes between which a first voltage is generated,wherein the first terminal of the first magnetoresistance element iscoupled to the first current passing node of the first transistor,wherein the first node of the first voltage source is coupled to thecontrol node of the first transistor and the second node of the firstvoltage source is coupled to the second terminal of the firstmagnetoresistance element, wherein the electronic circuit is operable togenerate a first current signal at the second current passing node ofthe first transistor related to a resistance value of the firstmagnetoresistance element, wherein the electronic circuit furthercomprises: a second magnetoresistance element having first and secondterminals; a second transistor having a control node, a first currentpassing node, and a second current passing node; a second voltage sourcehaving first and second nodes between which a second voltage isgenerated; and a load coupled to the second current passing node of thefirst transistor, wherein the second current passing node of the firsttransistor is coupled to the second current passing node of the secondtransistor, wherein the first terminal of the second magnetoresistanceelement is coupled to the first current passing node of the secondtransistor, wherein the first node of the second voltage source iscoupled to the control node of the second transistor and the second nodeof the second voltage source is coupled to the second terminal of thesecond magnetoresistance element, wherein the electronic circuit isoperable to generate a second current signal at the second currentpassing node of the second transistor related to a resistance value ofthe second magnetoresistance element, wherein a current passing throughthe load is equal to a difference between the first current signal andthe second current signal.
 28. The magnetic field sensor of claim 27,wherein the first voltage source comprises a reference leg of a currentmirror circuit.
 29. The magnetic field sensor of claim 27, furthercomprising: a comparator coupled to the second current passing node ofthe first transistor for generating a two state output signal.
 30. Amagnetic field sensor, comprising: a substrate; and an electroniccircuit disposed upon the substrate, the electronic circuit comprising:a first magnetoresistance element having first and second terminals; afirst transistor having a control node, and first current passing node,and a second current passing node; a first voltage source having firstand second nodes between which a first voltage is generated, wherein thefirst terminal of the first magnetoresistance element is coupled to thefirst current passing node of the first transistor, wherein the firstnode of the first voltage source is coupled to the control node of thefirst transistor and the second node of the first voltage source iscoupled to the second terminal of the first magnetoresistance element,wherein the electronic circuit is operable to generate a first currentsignal at the second current passing node of the first transistorrelated to a resistance value of the first magnetoresistance element,wherein the electronic circuit further comprises: a secondmagnetoresistance element having first and second terminals; a secondtransistor having a control node, a first current passing node, and asecond current passing node; and a second voltage source having firstand second nodes between which a second voltage is generated; a loadcoupled to the second current passing node of the first transistor,wherein the second current passing node of the first transistor iscoupled to the second current passing node of the second transistor,wherein the first terminal of the second magnetoresistance element iscoupled to the first current passing node of the second transistor,wherein the first node of the second voltage source is coupled to thecontrol node of the second transistor and the second node of the secondvoltage source is coupled to the second terminal of the secondmagnetoresistance element, wherein the electronic circuit is operable togenerate a second current signal at the second current passing node ofthe second transistor related to a resistance value of the secondmagnetoresistance element, wherein a current passing through the load isequal to a difference between the first current signal and the secondcurrent signal, wherein the electronic circuit further comprises: athird magnetoresistance element having first and second terminals; athird transistor having a control node, and first current passing node,and a second current passing node; and a third voltage source havingfirst and second nodes between which a third voltage is generated,wherein the first terminal of the third magnetoresistance element iscoupled to the first current passing node of the third transistor,wherein the first node of the third voltage source is coupled to thecontrol node of the third transistor and the second node of the thirdvoltage source is coupled to the second terminal of the thirdmagnetoresistance element, wherein the electronic circuit is operable togenerate a third current signal at the second current passing node ofthe third transistor related to a resistance value of the thirdmagnetoresistance element, wherein the electronic circuit furthercomprises: a fourth magnetoresistance element having first and secondterminals; a fourth transistor having a control node, a first currentpassing node, and a second current passing node; a fourth voltage sourcehaving first and second nodes between which a fourth voltage isgenerated; and a second load coupled to the second current passing nodeof the third transistor, wherein the second current passing node of thethird transistor is coupled to the second current passing node of thefourth transistor, wherein the first terminal of the fourthmagnetoresistance element is coupled to the first current passing nodeof the fourth transistor, wherein the first node of the fourth voltagesource is coupled to the control node of the fourth transistor and thesecond node of the fourth voltage source is coupled to the secondterminal of the fourth magnetoresistance element, wherein the electroniccircuit is operable to generate a fourth current signal at the secondcurrent passing node of the fourth transistor related to a resistancevalue of the fourth magnetoresistance element, wherein a current passingthrough the second load is equal to a difference between the thirdcurrent signal and the fourth current signal.
 31. The magnetic fieldsensor of claim 30, wherein the first voltage source and the thirdvoltage source are a same first common voltage source.
 32. The magneticfield sensor of claim 31, wherein the same first common voltage sourcecomprises a reference leg of a current mirror circuit.
 33. The magneticfield sensor of claim 31, wherein the second voltage source and thefourth voltage source are a same second common voltage source.
 34. Themagnetic field sensor of claim 33, wherein the same first common voltagesource comprises a reference leg of a current mirror circuit and whereinthe same second common voltage source comprises a common mode voltagedetector circuit coupled to the first and second loads and configured togenerate the first and third voltages as the same common-mode-relatedvoltage related to a common mode voltage between the first and secondloads.
 35. The magnetic field sensor of claim 30, wherein the secondvoltage source and the fourth voltage source are a same common voltagesource.
 36. The magnetic field sensor of claim 35, wherein the samecommon voltage source comprises a common mode voltage detector circuitcoupled to the first and second loads and configured to generate thefirst and third voltages as the same common-mode-related voltage relatedto a common mode voltage between the first and second loads.
 37. Themagnetic field sensor of claim 30, wherein the electronic circuitfurther comprises: a fifth magnetoresistance element having first andsecond terminals; a fifth transistor having a control node, and firstcurrent passing node, and a second current passing node; a fifth voltagesource having first and second nodes between which a first voltage isgenerated, wherein the first terminal of the fifth magnetoresistanceelement is coupled to the first current passing node of the fifthtransistor, wherein the first node of the fifth voltage source iscoupled to the control node of the fifth transistor and the second nodeof the fifth voltage source is coupled to the second terminal of thefifth magnetoresistance element, wherein the electronic circuit isoperable to generate a first current signal at the second currentpassing node of the fifth transistor related to a resistance value ofthe fifth magnetoresistance element, wherein the electronic circuitfurther comprises: a sixth magnetoresistance element having first andsecond terminals; a sixth transistor having a control node, an firstcurrent passing node, and a second current passing node; and a sixthvoltage source having first and second nodes between which a secondvoltage is generated; a load coupled to the second current passing nodeof the fifth transistor, wherein the second current passing node of thefifth transistor is coupled to the second current passing node of thesixth transistor, wherein the first terminal of the sixthmagnetoresistance element is coupled to the first current passing nodeof the sixth transistor, wherein the first node of the sixth voltagesource is coupled to the control node of the sixth transistor and thesecond node of the sixth voltage source is coupled to the secondterminal of the sixth magnetoresistance element, wherein the electroniccircuit is operable to generate a second current signal at the secondcurrent passing node of the sixth transistor related to a resistancevalue of the sixth magnetoresistance element, wherein a current passingthrough the load is equal to a difference between the first currentsignal and the second current signal, wherein the electronic circuitfurther comprises: a seventh magnetoresistance element having first andsecond terminals; a seventh transistor having a control node, and firstcurrent passing node, and a second current passing node; and a seventhvoltage source having first and second nodes between which a thirdvoltage is generated, wherein the first terminal of the seventhmagnetoresistance element is coupled to the first current passing nodeof the seventh transistor, wherein the first node of the seventh voltagesource is coupled to the control node of the seventh transistor and thesecond node of the seventh voltage source is coupled to the secondterminal of the seventh magnetoresistance element, wherein theelectronic circuit is operable to generate a third current signal at thesecond current passing node of the seventh transistor related to aresistance value of the seventh magnetoresistance element, wherein theelectronic circuit further comprises: an eighth magnetoresistanceelement having first and second terminals; an eighth transistor having acontrol node, a first current passing node, and a second current passingnode; an eighth voltage source having first and second nodes betweenwhich a fourth voltage is generated; and a second load coupled to thesecond current passing node of the seventh transistor, wherein thesecond current passing node of the seventh transistor is coupled to thesecond current passing node of the eighth transistor, wherein the firstterminal of the eighth magnetoresistance element is coupled to the firstcurrent passing node of the eighth transistor, wherein the first node ofthe eighth voltage source is coupled to the control node of the eighthtransistor and the second node of the eighth voltage source is coupledto the second terminal of the eighth magnetoresistance element, whereinthe electronic circuit is operable to generate a fourth current signalat the second current passing node of the eighth transistor related to aresistance value of the eighth magnetoresistance element, wherein acurrent passing through the second load is equal to a difference betweenthe third current signal and the fourth current signal.
 38. The magneticfield sensor of claim 37, wherein the first voltage source, the thirdvoltage source, the fifth voltage source, and the seventh voltage sourceare a same first common voltage source, the second voltage source andthe fourth voltage source are the same second common voltage source, andthe sixth and the eight voltage source are the same third common voltagesource.